4xAD1862/channel - summed 21 or 22 bit resulotion - combining all NR1, and NR2 pins?

Question

Dear Analog Devices Engineers! I would have a question about parallel DACs - [4x AD1862/channel] 1. Combining 4xNR1 pins? 2. And combining 4xNR2 pins? (Bias and voltage reference.) Power supply is the same. 
 Summed 21 or 22 bit resulotion. 
 Thank you for your reply. Laszlo

DaveThib · Accepted Answer

Hello TotoWood, 
 We did some experiments with doing this a few years back. First of all, you cannot just tie the pins together. You must sum the signals together actively. 
 Second, the AD1862 is an obsolete part. 
 We used an ADAU1966 and did experiments with combining two or more outputs and found that it really did not improve very much. We inverted the signal so that any common mode distortion and noise would cancel out when summed together. We got about a 3dB improvement in the SNR but more channels summed did not improve this much more. So, yes you can actively sum two DACs and get some improvement but it might not be worth the trouble. 
 Look into the AD1955. It is a high performance DAC to start with and perhaps summing two of those would give you some good results. Let us know how it goes if you do try it. 
 Dave T)

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4xAD1862/channel - summed 21 or 22 bit resulotion - combining all NR1, and NR2 pins?